US5654660A - Level shifted high impedance input multiplexor - Google Patents
Level shifted high impedance input multiplexor Download PDFInfo
- Publication number
- US5654660A US5654660A US08/534,420 US53442095A US5654660A US 5654660 A US5654660 A US 5654660A US 53442095 A US53442095 A US 53442095A US 5654660 A US5654660 A US 5654660A
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- US
- United States
- Prior art keywords
- input
- multiplexor
- buffer
- output
- channel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K19/00—Logic circuits, i.e. having at least two inputs acting on one output; Inverting circuits
- H03K19/02—Logic circuits, i.e. having at least two inputs acting on one output; Inverting circuits using specified components
- H03K19/173—Logic circuits, i.e. having at least two inputs acting on one output; Inverting circuits using specified components using elementary logic circuits as components
- H03K19/1733—Controllable logic circuits
- H03K19/1737—Controllable logic circuits using multiplexers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
- H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
- H03K17/687—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors
- H03K17/693—Switching arrangements with several input- or output-terminals, e.g. multiplexers, distributors
Definitions
- the present invention relates to integrated circuit design and in particular to the design of high density high impedance multiplexors.
- CMOS inverter When an CMOS inverter is driven from this less than full voltage swing signal, the P-channel device in the inverter is never turned completely off. This results in an undesirable DC current from the output of the inverter.
- One well known way of dealing with this unwanted current is to add a weak feedback inverter to raise the input level to the main inverter to Vdd and thereby allow the P-channel device in the inverter to shut off completely.
- FIG. 1 illustrates a prior art multiplexor which uses a feedback inverter to restore the input level to the main inverter.
- four N-channel switches 101, 103, 105 and 107 are connected to form a 4 to 1 multiplexor as is known in the art.
- Input signals IN1-IN4 are the signal inputs to the N-channel switches 101-107 respectively.
- Select signals S1-S4 control the gates of the N-channel switches 101-107, respectively, and serve to select which, if any, of the N-channel switches are turned to thereby allow the associated input signal to pass through the multiplexor.
- This inverter is designed as a standard CMOS inverter with a P-channel pull up transistor and a N-channel pull down transistor.
- the output of the main inverter becomes the circuit output 111.
- a weak feedback inverter 113 which has an input connected to the output of the main inverter.
- the output of the weak inverter is connected to the input of the main inverter (Node A).
- Inside the weak inverter is a two transistor CMOS inverter with the pull up and pull down transistors sized such that the output of the weak inverter can be overpowered by any of the N-channel switches 101-107 so the input to the main inverter can change.
- the P-channel pull up transistor in the weak inverter serves to pull up Node A to Vdd when a logic "1" is output on Node A by one of the N-channel switches.
- the weak inverter changes the input impedance of the N-channel switches 101-107. While a typical CMOS transistor has an input of approximately 10 14 ohms, since the output of the weak inverter is connected to Node A, the input impedance as seen by a device connected to any of the inputs IN1-IN4 is approximately (30*10 3 ) ohms. In FPGAs where the fanout may be very large and the series resistance of long interchip interconnect lines may be high, this low input impedance becomes a problem. In particular a transistor driving one of the N-channel switch inputs may not be able to supply the current required to drive the input at high speed, if at all.
- the present invention is a high input impedance multiplexor.
- a buffer stage is connected to a common output from a plurality of N-channel multiplexor switches.
- a pull up P-channel transistor in this buffer is connected to a voltage source which equals (Vdd--VtN-channel switch) such that the buffer output can be fully shut off when a logic "1" is output by one of the N-channel multiplexor switches.
- the output of the buffer is fed through an isolation N-channel transistor to a main inverter and weak feedback inverter.
- the input impedance as seen from a device driving a signal input to one of the N-channel multiplexor switches is approximately the input impedance of the buffer (high impedance).
- This novel circuit allows for the use of N-channel switching transistors while maintaining a high input impedance and eliminating unwanted output current.
- FIG. 1 illustrates a prior art CMOS 4 to 1 multiplexor.
- FIG. 2 illustrates a 4 to 1 CMOS multiplexor according to the present invention.
- FIG. 2 illustrates the preferred embodiment of the present invention.
- the common output "Node A" of the N-channel switches feeds the input of a buffer 201.
- Also connected to Node A are four series connected pull up P-channel transistors 203,205,207 and 209.
- the buffer 201 is constructed as a standard two transistor CMOS inverter with a P-channel pull up transistor and a N-channel pull down transistor. Instead of connecting the P-channel pull up transistor (inside 201) to Vdd as is normally done, the source of the P-channel transistor is connected to the drain 211 of a voltage drop N-channel transistor 213. The source and gate of transistor 213 are connected to Vdd.
- An isolation N-channel transistor 215 is connected in series between the buffer 201 output 217 and the junction 219 of the main inverter 109 input and weak inverter 113 output. The output of the main inverter 109 becomes the circuit output 221.
- the multiplexor switch transistors 101-107 operate as previously discussed in association with FIG. 1.
- the four pull up transistors 203-209 serve to keep Node A from “floating" when none of the mutiplexor switch transistors are selected (S1-S4 are at logic "0").
- the maximum voltage present on Node A when a multiplexor switch is selected is (Vdd-Vt N-channel) as already discussed. Since the source voltage 211 for the CMOS buffer is (Vdd-Vt of N-channel transistor 213) the signal on Node A is rail to rail with respect to the buffer. As such, the P-channel pull up transistor in buffer 201 is completely shut off when a logic "1" is output onto Node A by one of the multiplexor switch transistors.
- the output 217 of the buffer 201 is isolated from the higher voltage output of the weak inverter 113 by the series N-channel transistor 215.
- This transistor 215 keeps the drain of the P-channel pull up transistor inside buffer 201 from being at a higher voltage than the source voltage from the voltage drop transistor 213. This problem would occur without transistor 215 as the output of the weak inverter switches from rail to rail (Vdd to approximately 0.0 volts).
- the main inverter provides the circuit output 221 and the weak inverter performs a level restore function for the main inverter as discussed in association with FIG. 1.
- the input impedance as seen by a device driving one of the N-channel inputs IN1-IN4 is the input impedance of the buffer 201 which is approximately 10 14 ohms. Therefore this novel circuit allows the use of N-channel multiplexor switch transistors which is highly desirable in FPGAs while maintaining the high input impedance required for high fan out designs.
Abstract
Description
Claims (6)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/534,420 US5654660A (en) | 1995-09-27 | 1995-09-27 | Level shifted high impedance input multiplexor |
JP8252628A JPH09116405A (en) | 1995-09-27 | 1996-09-25 | Multiplexer |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/534,420 US5654660A (en) | 1995-09-27 | 1995-09-27 | Level shifted high impedance input multiplexor |
Publications (1)
Publication Number | Publication Date |
---|---|
US5654660A true US5654660A (en) | 1997-08-05 |
Family
ID=24129950
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US08/534,420 Expired - Fee Related US5654660A (en) | 1995-09-27 | 1995-09-27 | Level shifted high impedance input multiplexor |
Country Status (2)
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US (1) | US5654660A (en) |
JP (1) | JPH09116405A (en) |
Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5789966A (en) * | 1996-09-18 | 1998-08-04 | International Business Machines Corporation | Distributed multiplexer |
EP0926828A1 (en) * | 1997-12-25 | 1999-06-30 | Sharp Kabushiki Kaisha | Semiconductor integrated circuit |
US5982220A (en) * | 1996-12-27 | 1999-11-09 | Hyundai Electronics Industries Co., Ltd. | High speed multiplexer circuit |
US6087855A (en) * | 1998-06-15 | 2000-07-11 | International Business Machines Corporation | High performance dynamic multiplexers without clocked NFET |
WO2001040947A1 (en) * | 1999-12-06 | 2001-06-07 | Infineon Technologies North America Corp. | Fuse latch having multiplexers with reduced sizes and lower power consumption |
WO2001045260A1 (en) * | 1999-12-14 | 2001-06-21 | Koninklijke Philips Electronics N.V. | Electronic component with reduced inductive coupling |
US20030076821A1 (en) * | 2001-10-19 | 2003-04-24 | Fujitsu Limited | Multiplexer circuit for converting parallel data into serial data at high speed and synchronized with a clock signal |
US20050083107A1 (en) * | 2003-07-28 | 2005-04-21 | Elixent Limited | Methods and systems for reducing leakage current in semiconductor circuits |
WO2011035519A1 (en) * | 2009-09-23 | 2011-03-31 | 惠州市正源微电子有限公司 | Radio frequency power synthesis circuit |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP4883578B2 (en) * | 2007-05-11 | 2012-02-22 | 独立行政法人産業技術総合研究所 | Multiplexer circuit |
Citations (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4806786A (en) * | 1987-11-02 | 1989-02-21 | Motorola, Inc. | Edge set/reset latch circuit having low device count |
US4820939A (en) * | 1987-11-24 | 1989-04-11 | National Semiconductor Corporation | Finite metastable time synchronizer |
US5046047A (en) * | 1989-02-10 | 1991-09-03 | Plessey Overseas Limited | Circuit arrangement for verifying data stored in a random access memory |
US5099143A (en) * | 1988-10-15 | 1992-03-24 | Sony Corporation | Dual voltage supply circuit with multiplier-controlled transistor |
US5164612A (en) * | 1992-04-16 | 1992-11-17 | Kaplinsky Cecil H | Programmable CMOS flip-flop emptying multiplexers |
US5173870A (en) * | 1989-03-09 | 1992-12-22 | Mitsubishi Denki Kabushiki Kaisha | Transmission and latch circuit for logic signal |
US5173626A (en) * | 1990-06-25 | 1992-12-22 | Kabushiki Kaisha Toshiba | Flip-flop with scan path |
US5264738A (en) * | 1991-05-31 | 1993-11-23 | U.S. Philips Corp. | Flip-flop circuit having transfer gate delay |
EP0637132A2 (en) * | 1993-07-30 | 1995-02-01 | Nec Corporation | Simple temporary information storage circuit controllable with enable/reset signal |
US5467038A (en) * | 1994-02-15 | 1995-11-14 | Hewlett-Packard Company | Quick resolving latch |
US5504919A (en) * | 1993-02-19 | 1996-04-02 | National Science Council | Sorter structure based on shiftable content memory |
-
1995
- 1995-09-27 US US08/534,420 patent/US5654660A/en not_active Expired - Fee Related
-
1996
- 1996-09-25 JP JP8252628A patent/JPH09116405A/en active Pending
Patent Citations (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4806786A (en) * | 1987-11-02 | 1989-02-21 | Motorola, Inc. | Edge set/reset latch circuit having low device count |
US4820939A (en) * | 1987-11-24 | 1989-04-11 | National Semiconductor Corporation | Finite metastable time synchronizer |
US5099143A (en) * | 1988-10-15 | 1992-03-24 | Sony Corporation | Dual voltage supply circuit with multiplier-controlled transistor |
US5046047A (en) * | 1989-02-10 | 1991-09-03 | Plessey Overseas Limited | Circuit arrangement for verifying data stored in a random access memory |
US5173870A (en) * | 1989-03-09 | 1992-12-22 | Mitsubishi Denki Kabushiki Kaisha | Transmission and latch circuit for logic signal |
US5173626A (en) * | 1990-06-25 | 1992-12-22 | Kabushiki Kaisha Toshiba | Flip-flop with scan path |
US5264738A (en) * | 1991-05-31 | 1993-11-23 | U.S. Philips Corp. | Flip-flop circuit having transfer gate delay |
US5164612A (en) * | 1992-04-16 | 1992-11-17 | Kaplinsky Cecil H | Programmable CMOS flip-flop emptying multiplexers |
US5504919A (en) * | 1993-02-19 | 1996-04-02 | National Science Council | Sorter structure based on shiftable content memory |
EP0637132A2 (en) * | 1993-07-30 | 1995-02-01 | Nec Corporation | Simple temporary information storage circuit controllable with enable/reset signal |
US5467038A (en) * | 1994-02-15 | 1995-11-14 | Hewlett-Packard Company | Quick resolving latch |
Cited By (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5789966A (en) * | 1996-09-18 | 1998-08-04 | International Business Machines Corporation | Distributed multiplexer |
US5982220A (en) * | 1996-12-27 | 1999-11-09 | Hyundai Electronics Industries Co., Ltd. | High speed multiplexer circuit |
US6271685B1 (en) | 1997-12-25 | 2001-08-07 | Sharp Kabushiki Kaisha | Semiconductor integrated circuit |
EP0926828A1 (en) * | 1997-12-25 | 1999-06-30 | Sharp Kabushiki Kaisha | Semiconductor integrated circuit |
US6087855A (en) * | 1998-06-15 | 2000-07-11 | International Business Machines Corporation | High performance dynamic multiplexers without clocked NFET |
WO2001040947A1 (en) * | 1999-12-06 | 2001-06-07 | Infineon Technologies North America Corp. | Fuse latch having multiplexers with reduced sizes and lower power consumption |
US6693785B1 (en) * | 1999-12-14 | 2004-02-17 | Koninklijke Philips Electronics N.V. | Electronic component with reduced inductive coupling |
WO2001045260A1 (en) * | 1999-12-14 | 2001-06-21 | Koninklijke Philips Electronics N.V. | Electronic component with reduced inductive coupling |
US20030076821A1 (en) * | 2001-10-19 | 2003-04-24 | Fujitsu Limited | Multiplexer circuit for converting parallel data into serial data at high speed and synchronized with a clock signal |
US7154918B2 (en) | 2001-10-19 | 2006-12-26 | Fujitsu Limited | Multiplexer circuit for converting parallel data into serial data at high speed and synchronized with a clock signal |
US20050083107A1 (en) * | 2003-07-28 | 2005-04-21 | Elixent Limited | Methods and systems for reducing leakage current in semiconductor circuits |
US7233197B2 (en) | 2003-07-28 | 2007-06-19 | Panasonic Europe Ltd. | Methods and systems for reducing leakage current in semiconductor circuits |
US20070241811A1 (en) * | 2003-07-28 | 2007-10-18 | Alan Marshall | Methods and Systems for Reducing Leakage Current in Semiconductor Circuits |
US7315201B2 (en) | 2003-07-28 | 2008-01-01 | Panasonic Europe Ltd. | Methods and systems for reducing leakage current in semiconductor circuits |
WO2011035519A1 (en) * | 2009-09-23 | 2011-03-31 | 惠州市正源微电子有限公司 | Radio frequency power synthesis circuit |
CN101667854B (en) * | 2009-09-23 | 2013-02-13 | 惠州市正源微电子有限公司 | Radio-frequency power composite circuit |
Also Published As
Publication number | Publication date |
---|---|
JPH09116405A (en) | 1997-05-02 |
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Owner name: HEWLETT-PACKARD COMPANY, CALIFORNIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:ORGILL,RODNEY H.;MASON,WILLIAM R.;REEL/FRAME:007990/0039 Effective date: 19951206 |
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Owner name: HEWLETT-PACKARD COMPANY, A DELAWARE CORPORATION, C Free format text: MERGER;ASSIGNOR:HEWLETT-PACKARD COMPANY, A CALIFORNIA CORPORATION;REEL/FRAME:010841/0649 Effective date: 19980520 |
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Owner name: AGILENT TECHNOLOGIES INC, CALIFORNIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:HEWLETT-PACKARD COMPANY;REEL/FRAME:010977/0540 Effective date: 19991101 |
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Year of fee payment: 4 |
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LAPS | Lapse for failure to pay maintenance fees | ||
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Free format text: PATENT EXPIRED FOR FAILURE TO PAY MAINTENANCE FEES (ORIGINAL EVENT CODE: EXP.); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY |
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STCH | Information on status: patent discontinuation |
Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362 |
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FP | Lapsed due to failure to pay maintenance fee |
Effective date: 20050805 |